Medical devices may be coated so that the surfaces of the devices have desired properties or effects. For example, it may be useful to coat medical devices to provide for the localized delivery of therapeutic agents to target locations within the body, such as to treat localized disease (e.g., heart disease) or occluded body lumens. Localized drug delivery may avoid some of the problems of systemic drug administration, which may be accompanied by unwanted effects on parts of the body which are not to be treated. Additionally, treatment of the afflicted part of the body may require a high concentration of therapeutic agent that may not be achievable by systemic administration. Localized drug delivery may be achieved, for example, by coating balloon catheters, stents and the like with the therapeutic agent to be locally delivered. The coating on medical devices may provide for controlled release, which may include long-term or sustained release, of a bioactive material.
Aside from facilitating localized drug delivery, medical devices may be coated with materials to provide beneficial surface properties. For example, medical devices are often coated with radiopaque materials to allow for fluoroscopic visualization during placement in the body. It is also useful to coat certain devices to achieve enhanced biocompatibility and to improve surface properties such as lubriciousness.
Spray coating of stents may require a method of holding the stents that does not block the spray plume from uniformly coating the entire stent. Reducing contact with the stent and the desire to securely hold the stent may complicate the problem of clamping since the stent is subject to the forces from the spray plume itself. Excessive contact with the stent by the fixture during the spray coating operation may cause gaps in the coating that may result in loss of the coating during loading, shipping, and/or deployment of the stent. The coating may not adhere to the stent directly, and may only bind to itself, in which case the quality of the coating may depend on the coating being relatively uniform and relatively complete over the whole surface of the stent.
The flexible nature of the stent may require a clamping mechanism (also referred to herein as a fixing or affixing mechanism) that holds the stent from within to prevent the stent from sagging during the spraying operation. Coating self expanding stents greater than 40 mm may be difficult with current fixtures. Spray coating a stent that may be flimsy due to low stiffness and/or large size may be difficult due to the lack of rigidity of the stent itself. The lack of rigidity may make holding the stent complicated.
A fixture for mounting the stent(s) in the spray plume may meet the following criteria. The fixture may not block the spray plume from uniformly coating the entire stent. The number of contact points may be kept to a minimum to avoid causing bare spots in the coating. The fixture may hold the stent securely to prevent sagging of the center and/or ends when subjected to the forces from the spray plume (sagging of the stent may cause movement and may lead to poor coating). The loading and unloading of the fixture may be simple to keep handling damage to a minimum. The fixture may be easy to manufacture.
Some stent fixtures may be unable to hold a flimsy stent against the force of gravity and/or the spray plume. An extended version of a existing fixture has been used, but the conventional fixture may allow movement of the center of the stent, causing wavy and inconsistent coating through the middle and distal (loosest) end of the stent.
There thus is a need for a device for holding a stent during a coating operation that supports the stent against the forces of the coating operation and that does not inhibit the coating process.